Age-related macular degeneration (ARMD) is a cause of irreversible blindness in elderly populations, in particular in Europe and in North America. ARMD affects the central part of the retina, called the macula, leading to a serious visual deficiency and the irreversible loss of central vision.
The macular function is responsible for central vision and visual acuity, the high resolution of which is linked to its high concentration of cone photoreceptors. The early stage of ARMD is marked by deposits called Drusen, which only marginally affect sight. The subsequent phases comprise two forms of ARMD, geographical atrophy (dry form) or exudative atrophy (wet or neovascular form), the first being much more common than the second. The final steps of these two forms result in the destruction of the macular neurosensory retina, but the progression of dry ARMD is generally slow, while wet ARMD can result in complete blindness in a few weeks.
Aging is the gradual accumulation over time of changes which are associated with (or responsible for) increasing susceptibility to the disease. In the retina, a certain number of degenerative diseases, including glaucoma, retinitis pigmentosa and ARMD, can occur following aging. Retinis pigmentosa groups together a heterogeneous set of genetic retinal degenerations, involving the photoreceptors and the RPE, and resulting in a loss of nocturnal vision, then later on of central vision. Although the specific mechanisms involved in the initiation of various types of diseases related to retinal aging differ, it is thought that the oxidative stress and the inflammation that result therefrom are important elements which contribute to the pathogenesis.
The theories about the etiology of ARMD include hydrodynamic modifications in Bruch's membrane caused by a gradual accumulation of extracellular material containing lipids, and senescence of the RPE, the activity of which is essential to the survival of the photoreceptors. The cells of the RPE have several different functions in the eyes: they establish the blood-retinal barrier through their tight junctions, and are thus responsible for the immunoprivileged status of the interior part of the eyeball; they keep the photoreceptors alive by providing them with nutrients and participate in the visual cycle. The current understanding is that a deficiency in the function of the cells of the RPE is responsible for the development of ARMD. The aging causes a dysfunction of the RPE cells and an insufficiency of their metabolism, and also of their phagocytic activity. Incomplete digestion of the external segments of the photoreceptors can result in the formation of Drusen by reducing the diffusion across the Bruch's membrane, which firstly causes a deformation of the retina and of the perceived images.
With age, the RPE stores an increasing amount of lipofuscins. These are composed of lipids and proteins, which originate from the phagolysosomes, lysosomes and photoreceptors. Lipofuscins also contain N-retinyl-N-retinylidene ethanolamine (A2E), which is formed by the condensation of two retinaldehyde molecules with ethanolamine.
Aging is accompanied by an increased accumulation of A2E in the retina (Bhosale et al., 2009). Under the action of blue light and in the presence of oxygen, A2E generates reactive species which cause damage to the proteins, to the lipids and to the DNA, and thus a significant oxidative stress in the aging cells of the RPE (Sparrow & Cai, 2001). This damage disrupts the lysosomal activity of cells of the RPE and causes an accumulation of waste, which ends up causing, from place to place, the death of cells of the RPE, which is followed by that of the photoreceptors with which they were associated.
No medicament exists on the market for the treatment of dry ARMD, whereas medicaments by intravitreal injection of anti-VEGF (Vascular Endothelial Growth Factor) antibodies are sold, making it possible to partially block the formation of neovessels and thus offering an alternative treatment for wet ARMD. Food supplements have been formulated with generic antioxidant compounds, namely minerals and vitamins with antioxidant properties, for example zinc, vitamins A, C, E, with an actual but limited therapeutic efficacy. The AREDS nutraceutical formula 1 (“Age-Related Eye Disease Study”, AREDS 2001) is considered to be the standard for care in the United States for the treatment of dry ARMD, reducing the risk of advanced ARMD by 25% and sight loss by 19% over five years.
Numerous products propose a common formulation base: zinc and vitamins C and E, to which are added various ingredients: lutein, resveratrol, omega-3 fatty acids, without however providing convincing data about efficacy with regard to these additional ingredients, or with regard to the categories of patients who may respond favorably to these various molecules (Elliot & Williams, 2012). In particular, in the prior art, there is international application WO 2005/110375 which relates to a food supplement intended to limit them or prevent the loss of visual acuity of ocular after effects of a disease.
Carotenoids (molecules exclusively provided by the diet) have been more particularly studied, since some of them (lutein, zeaxanthin=xanthophylls) are naturally present in the macula (Subczynski et al., 2010), and it is known that these compounds have a strong anti-oxidizing power. It is thus logical for these compounds to have been tested (alone or in combination) in the AREDS formula, but the results obtained were limited, the supplementation proving to be efficacious only for a subset of patients with a deficiency in these compounds (Pinazo-Duran et al., 2014). These molecules are efficacious in vitro for protecting cells of the RPE (Human D407) against the toxic effects of hydrogen peroxide (Pintea et al., 2011).
Japanese patent application JP 2010285364 puts forward a mixture composed of crocetin and of another carotenoid that can be a xanthophyll or another diapocarotenoid, i.e. bixin or norbixin. This mixture, owing to its anti-oxidizing properties, is proposed for relieving or preventing diseases in which an oxidative phenomenon is involved.
Other xanthophylls have also been the subject of studies by oral supplementation, alone or in combination with lutein and/or zeaxanthin (for example astaxanthin—Parisi et al., 2008). Recently, diapocarotenoids (=carotenoids truncated at the two ends—IUPAC chemical nomenclature) have been tested in vitro and in vivo, in particular crocetin (=8,8′-diapocarotene-8,8′-dioate) and glycosides thereof (crocins). Crocins have an in vitro photoprotective effect on primary cultures of bovine or primate photoreceptors (Laabich et al., 2006), and crocetin protects neuroganglion cells against oxidative stress (Yamauchi et al., 2011). Saffron (a spice rich in crocins/crocetin) administered orally has proved to be active in vivo on the quality of the retina (Maccarone et al., 2008; Falsini et al., 2010; Boisti et al., 2014). However, since saffron contains other molecules that may be active on the retina, such as other carotenoids and also safranal formed at the same time as crocetin (Verma & Middha, 2010; Fernández-Sánchez et al., 2012), it is difficult to reach a conclusion with regard to the effect of crocetin alone.
Experiments have also been carried out with another apocarotenoid, bixin (=methylhydrogen 6,6′-diapocarotene-6,6′-dioate) or certain derivatives thereof, in vitro on neuroganglion cells and in vivo by intravitreal injections to counteract the effects of a stress of the endoplasmic reticulum (Tsuruma et al., 2012). The tests thus carried out most commonly evaluate an anti-oxidizing and thus protective activity of the compounds with respect to various cell types of the retina subjected to the presence of an oxidizing agent (for example hydrogen peroxide), and they are not therefore directly within the context of ARMD.
An extract of Urucum (Bixa orellana) seeds previously developed (Bixilia®) has shown a photoprotective effect on human skin exposed to UV radiation (FR 2947173, Veillet et al., 2009) and on RPE cells subjected to a photo-oxidizing stress (Fontaine et al., 2011). The Bixilia® extract is a natural extract of Urucum which has been enriched with bixin. Bixilia® contains other photoprotective compounds of phenolic nature, the presence of which might explain the greater photoprotective activity of the crude extract compared with bixin alone. In patent FR 11 54172 (Fontaine et al., 2011), the protective effect on RPE cells of some of the compounds of the Bixilia® extract is analyzed. The results of the tests using bixin or norbixin at the concentrations 0.1 micromolar (μM), 1 μM and 10 μM do not have any photoprotective activity and even imply that the higher the bixin or norbixin concentration, the less the RPE cells survive and therefore the weaker is the photoprotective effect. It is noted, inter alia, that substances such as cyanidin and ellagic acid at concentrations of 10 μM and 20 μM have an advantageous photoprotective effect on RPE cells.
A more thorough study has led to the active molecules present in the Bixilia® extract being identified and to their mechanism of action being specified, and then to their efficacy in vivo being demonstrated in mice and rats. This study has given rise to the present invention. The invention thus envisions finding a treatment for protecting RPE cells that is an alternative to those that already exist.